There have been proposed and used a number of gases and liquids for treating eye disorders. Liquids that have been used as intraocular tools include silicone oils (polydimethysiloxanes), fluorosilicone oils such as polymethyl-3,3,3-trifluoropropylsiloxane and a number of perfluorocarbon liquids, for example perfluorooctane, perfluorodecalin and perfluorophenanthrene (perfluorotetradecahydrophenanthrene).
One use of these liquids is in vitreoretinal surgery. The properties of the liquid for such use should be that it is transparent with a refractive index close to that of the vitreous. The substance should not mix with the vitreous, nor should it disperse or emulsify in the vitreous. Of course it should also be chemically and physiologically inert. To effectively act as a retinal tamponade, the substance should have a high interfacial tension and a high surface tension.
Silicone oils have been used for a number of years in vitreoretinal surgery. They are also known to be used for treating other disorders of the eye as set forth in U.S. Pat. No. 4,490,351, incorporated herein by reference. Silicone oil is transparent with a refractive index of 1.404 (the refractive index of water is 1.33), and a specific gravity of 0.97. It has a relatively high interfacial and surface tension, making it useful as a retinal tamponade. However, because the specific gravity of silicone oil is less than that of water, it is not useful as a tamponade for an inferior detached retina. Further, the viscosity of the silicone oils commonly used in vitreoretinal surgery is from 1,000 to 12,000 cs. The high viscosity makes it relatively difficult to handle, requiring the surgeon to use a silicone oil pump to pump the liquid through the needle in to and out of the eye.
Fluorosilicone oil has a higher specific gravity of 1.29 and also has a relatively high surface and interfacial tension. The fluorosilicone oils in experimental use have a viscosity in the same range as the silicone oil. Accordingly, they are just as difficult to work with. An additional problem with the fluorosilicone oils, however, is its tendency to emulsify in the eye. It appears that the dispersion of the fluorinated oil is stabilized in the eye by surface active proteins that interact with the highly electronegative fluorine atoms pendant on the polysiloxane backbone. Accordingly, fluorosilicone oils do not appear to be useful as long-term vitreous replacements for vitreoretinal surgery.
A number of perfluorocarbon liquids have also been investigated for treating eye disorders, particularly for intravitreous surgery. The relatively high specific gravity of about 2 makes them useful as an inferior detached retina tamponade. The high density could however damage the sensitive retinal tissue. In addition, the viscosity of the fluorocarbon liquids is only from about 1 to 8 cs, leading to more potential for emulsification in the vitreous. Further, the extremely high specific gravity also increases the chances of dispersion of the liquid in the vitreous. This dispersion, or "fish egging", of the perfluorocarbon liquids is more pronounced because of the number of fluorine atoms present in the compound that act to stabilize the dispersed liquid droplets. Accordingly, these liquids must be replaced in a second surgical procedure soon after the first repair procedure.
The use of silicone oil and perfluorocarbon liquids together has also been studied. See, for example, Ophthalmic Surgery "Long-Term Vitreous Replacement in Primates with Intravitreal Vitreon or Vitreon Plus Silicon", G. A. Peyman et al., V. 22, No. 11, November 1991, pages 657-664; Retina "Experimental Studies of the Combined Use of Vitreous Substitutes of High and Low Specific Gravity", J. R. Sparrow et al., V. 12, No. 2, 1992, pages 134-140. The silicone oil is useful as a tamponade for superior retinal detachments, and the perfluorocarbon for inferior retinal detachments. The use of the two together provides tamponade and mechanical support of both portions of the retina simultaneously. However, since the liquids are immiscible, the volumes of each must be carefully controlled for effective use. In addition, the great viscosity and density differences between the liquids leads to a greater tendency toward dispersion, which is offset to some extent by the lower fluorine concentration as compared to pure perfluorocarbon liquid (but not as compared to pure silicone oil). Because perfluorocarbons are used, however, this procedure requires that the tamponade be relatively quickly removed and replaced in a second surgical procedure.